The present invention pertains to a method of creating active finite elements for studying mechanical properties of active structures. One of the applications is to study the mechanical properties of skeletal muscles, which is important to industrial design of sport, automotive, medical and health equipment for exercise, rehabilitation and treatments, for example.
The basic ideas of the finite element method are presented in a paper “Stiffness and Deflection Analysis of Complex Structures” in 1956. In 1960, the name “finite element” was coined by R. W. Clough in a paper “The Finite Element Method in Plane Stress Analysis” on plane elasticity problems. The finite element method uses numerical analysis to obtain approximate solutions for solving various engineering problems. A structure or region to be analized is broken down into many small and interconnected subregions. These subregions are called finite elements.
Traditionally, the finite element method has been frequently used in design processes in civil, mechanical and aeronautical engineering. Recently, the finite element method has been successfully extended to solve other types of engineering problem, like geomechanics, acoustics, electromagnetic fields, field dynamics and heat transfer. Some attention has also been given to the micro- and macro-analyses of advanced composite materials.
In stress/displacement finite element analyses, external conditions such as boundary conditions and loads can be prescribed on nodes, element faces and element bodies. Boundary conditions generally include prescribed displacement, prescribed velocity and prescribed acceleration. Loads can include concentrated forces, surface tractions, moments, and body forces due to centrifugal acceleration, rotary acceleration, and gravity. When all nodes in a node set are prescribed a displacement in certain degrees of freedom, these nodes will displace from their original positions in the prescribed direction after a specified time period. When a surface traction such as pressure force is applied onto the surface of an element set, these elements may deform, displace or rotate. Thus, if no appropriate external conditions are prescribed on them, any nodes or elements are passive and do not have any motion.
However, some structures like skeletal muscle are active in nature. Whenever there is an electrical stimulation applied to skeletal muscle, the muscle can contract under no prescribed externally applied displacement and load. As material properties of current finite elements are limited to be passive, simulation of active structures and the interactions with passive ones are almost impossible to perform. Thus, the foregoing calls for a novel method to model the mechanical properties of active structures like human beings, animals, and smart structures.